Oral contraceptives can cause falsely low vitamin B-12 levels

Serum vitamin B-12 radioimmunoassays may give falsely low results in patien ts with folate deficiency, multiple myeloma, megadose of vitamin C and foll owing radioisotope organ scan. We evaluated 10 consecutive healthy women on oral contraceptives (OC) who had falsely low vitamin B-12 levels, as refle cted by normal urine methylmalonic acid and plasma homocysteine. After 1-mo nth cessation of OCs, vitamin B-12 returned to the normal range in all wome n. Transcobalamin I (TCI) blood level was decreased in 60% of patients. OCs may cause temporary low vitamin B12 blood levels of no clinical significan ce that can be associated with low TCI levels Copyright (C) 2000 S. Karger AG, Basel.